The present invention relates in general to an ink monitor system and pertains, more particularly, to an improved system for monitoring the weight of ink consumed, particularly as it relates to a high-speed, web-fed printing operation.
Continuous high-speed web-fed printing presses produce printed product at a very high rate. They also consume materials, primarily ink and paper, at a very high rate. While the gross consumption of ink can be determined after the fact by examining the amount of ink purchased less that remaining in inventory or the number of cans, barrels, etc. consumed in the course of a week or a month, there is no effective way of measuring ink consumption and allocating that consumption accurately to the various points in the printing process at which ink is consumed.
To understand the problem, one can consider a typical ink-consuming machine, a web offset printing press. The press comprises a paper supply, usually in the form of a roll stand and automatic splicing device that provides paper to the press continuously from a sequence of paper supply rolls. A web tensioning device and a sequence of printing units, usually not less than four nor more than eight, print images of different colors on the web in succession. At the end of the printing units is equipment for causing the ink to set and for either rewinding the product or dividing the web into individual products through a combination of folding and cutting processes.
Each printing unit has two lithographic plate cylinders, each of which is coupled with a blanket cylinder for the purpose of transferring an inked image from the plate to the paper. The two blanket cylinders have surfaces of a resilient rubber-like characteristic and engage each other along a nip, through which the paper passes and, in so doing, have the inked images from both blanket cylinders transferred to its surface.
The plate cylinders carry plates having the image information on their surface in the form of differentiated wetting properties for oil and water. In rotating from one engagement with the blanket cylinder to the next, an element of the plate cylinder first moves under the dampening system which places a thin, uniform film of water on all parts of the plate cylinder that are susceptible to being wetted. It then passes under the ink system. A second series of rollers delivers a uniform, thin film of ink to those areas of the plate that have been sensitized to receive ink and reject water.
The source of ink is a tray disposed crosswise of the web, one side of which is formed by or supports a roller. The bottom of the tray has a thin plate or a blade, having an adjustable clearance with the roller, so that as the roller turns, it has deposited upon it a film of ink whose thickness is controllable by adjusting the blade clearance. The blade may be flexible, or formed of segments, to print differential control of ink film thickness across the web. The ink, so supplied to the roller, is delivered through a series of contacting rollers to the plate. The quantity of ink delivered to the plate may be varied by adjusting the ink film delivered to the fountain roller.
In the printing process, the fountain blade is adjusted so that the ideal amount of ink is delivered by the fountain to produce the correct color density in the printed image. In practice, however, the amount of ink delivered may vary from the ideal. And while a deficiency of ink is usually readily apparent, an appreciable excess can be delivered without greatly affecting the image quality. Thus, it is desirable to measure directly the quantity of ink being applied at each fountain.
In setting prices for printing work, it is necessary to estimate total quantities of paper, ink, labor, and press time to be consumed in completing the job. In the performance of the work, it is also desirable to measure the actual quantities used in order to compare with the estimate, to determine the profitability of the particular job and the accuracy of the estimating procedure. While means exist for the measuring of time, labor, and paper consumption, the measurement of ink consumption is a much less satisfactory procedure, especially when ink is supplied continuously to a multiplicity of jobs by pumping from large tanks. Ink is bought by the pound and has a variable density so volumetric flow meters offer a poor approximation to the ink used.
Accordingly, it is an object of the present invention to measure accurately the total quantity of ink delivered to each job, for each color used, and to indicate the rate of pounds of ink consumption at each consuming point associated with the press.
Existing systems for the measurement of ink consumption typically rely on metering devices in the ink lines supplying a whole press. When displacement-type meters are used, it is necessary to convert the volume of ink used to weight, using the density of the ink. However, ink densities vary widely, not only from color-to-color, brand-to-brand, and lot-to-lot within a brand, but also the ink drawn from a given container may vary in density, so that even if each ink container is sampled, the method is still inaccurate. A true mass rate flowmeter would overcome this, and attempts have been made to employ so-called mass sensing meters but without success. Even if a mass rate meter compatible with inks were to be developed, it would suffer from the drawback of all feed line metering systems; the inability to attribute the ink to the individual consuming points to know how much was used at each fountain. While this could theoretically be overcome by use of a mass rate flowmeter at the line feeding each individual fountain, the number of meters so required would be large, and the system uneconomic as a result.
Accordingly, it is a further object of the present invention to provide indication of the weight of ink consumed at each fountain of a web offset press having many such fountains and to provide the indication of weight, independent of density variations in the ink, and without requiring that sensors be installed at each fountain.
A further object of the present invention is to provide an ink monitor system for indicating the rate of ink consumption in weight of ink per thousand printed products at each ink consuming position in the press.
Still another object of the present invention is to provide an ink monitor system that provides a remote indication of the amount of ink in each tank in use for supplying ink to the press.
Another object of the present invention is to provide an ink monitoring system having alarms when the ink has reached a predetermined low level so that provision of a replacement tank can take place.